Question

define valency and how will you predict the valence of the atom?​

Answer 1

Valency refers to the ability of an atom or a group of chemically bonded atoms to form chemical bonds with other atoms or groups of atoms. 

The valency of an element is determined by the number of outer shell (valence) electrons.

The valency of polyatomic ions (such as SO42- ) is the charge on the ion.

Answer 2

Valency of an atom means the number of unpaired electrons in the last shell or the valence shell of an atom.

If the number of electrons in valence shell are 1, 2, 3 and 4, then it is the valency of an atom.

If the number of electrons in valence shell are more than 4 i.e. 5, 6 and 7; then the valency is

8 - the no. Of electrons in valence shell.

Ex.

1.Sodium:

atomic number = 11

Valency = +1

2. Carbon:

Atomic number = 4

Valency = 4

3. Chlorine:

Atomic number = 17

Valency = - 1